Process for fabricating arc tubes



Nov. 15, 1966 F. A. LOUGHRIDGE PROCESS FOR FABRICATING ARC TUBES Filed Feb. 4, 1963 u. S G w m T G .Hn I I 1. A F 6 K 2 I m R E D E R F FIG.9

A TORNEY United States Patent ware Filed Feb. 4, 1963, Ser. No. 256,049 Claims. (CI. 65-32) This invention relates to the fabrication of high pressure discharge devices and more particularly to the fabrication of iodine-containing discharge devices.

Techniques have previously been disclosed for the fabrication of high pressure discharge devices. Suchdevices however differ from the iodine-containing devices in that the former emit radiation of only a few distinct wavelengths whereas the latter emits a large number of very closely spaced lines. The emission color of conventional high pressure discharge devices, generally called mercury lamps in the art, is a bluish-green. But the iodine-containing devices emit a white light however due to the large number of closely spaced emission lines. Color rendition of the iodine-containing lamps is materially improved and hence making them is highly desirable. But certain problems have presented themselves to the art and I have discovered that the iodine-containing devices suifer quite markedly from the inclusion of any appreciable concentrations of hydrogen in the arc tube. Formation of a stable arc in the arc tube is made extremely difi'icult since the starting voltages are raised materially. It is believed that these difficulties are due to the formation of hydrogen iodide which has a much higher vapor pressure than any other iodide present in the system. For every atom of hydrogen present, it is reasonable to expect that there will be an extra atom of iodine in the vapor state. And when the atoms of iodine are present in the vapor state, starting is made more difficult. Now it is known to the art of course, that hydrogen should be excluded from the conventional mercury lamps or more practically, the amount should be reduced to the lowest possible limits. But with'these conventional lamps, minor quantities of hydrogen such as might enter the arc tube during sealing are not particularly deleterious; However as I have indicated, the problem of hydro gen is presented more acutely in the iodine-containing lamps. I

I have discovered that much of the hydrogen can be eliminated from the arc tube if the conventional sealing techniques aremodified. According to my invention I have discovered that one of the major sources of hydrogen contamination is the combustion gases produced during heating and sealing of the arc tube. Products of combustion in ordinary burners using either natural or manufactured gas included in addition to carbon dioxide and water, a quantity of carbon monoxide, low boiling hydrocarbons such as methane and ethane, and also the deleterious hydrogen together with some oxygen. With conventional techniques these combustion gases tended to flow along the outside of the unsealed arc tube cylinder and even though a positive pressure of nitrogen was maintained inside, the hydrogen interdiffused with the nitrogen and was entrapped in the arc tube after sealing. But I have discovered that when the arc tube cylinder is appreciably extended and preferably necked down at or below the point where the seal is to be made, the hydrogen cannot flow substantially into the arc tube. Additionally, when the unsealed arc tube is shielded above the end thereof but below the point Where the sealing flame impinges and preferably substantially proximate to the 'impingernent point, the interruption is made in the normal flow pattern of the gases and interdiffusion of the nitrogen-fill gas and hydrogen is reduced materially. Furthermore, when the scaling is made at the lower end of the are tube cylinder, rather than the top as is generally done in the art, a further reduction in hydrogen contamination is accomplished.

Accordingly, the primary object of my inventionis to prevent the entrance of hydrogen during sealing into an arc tube which can be used in a high pressure discharge device.

A feature of my invention is the use of long extensions on the ends of the arc tube cylinder together with flowing therethrough nitrogen'or another gas inert to the arc tube and itscomponents.

A further feature of my invention is disrupting the normal flow path of combustion gases from the heating burners by the use of an arc tube extension.

Another feature of my invention is necking down the extension'on the arc tube cylinder to reduce the amount of combustion gas which can enter the arc tube cylinder and also to reduce glass costs.

Many other advantages, features and objects of the present invention will become manifest to those conversant with the art, upon making reference to the detailed description which follows and the accompanying sheet of drawings in which a preferred procedural embodiment of a method of fabricating a high pressure discharge device arc tube is shown and described, and wherein the principles of the present invention are incorporated by way of illustrative examples.

The drawings are in the nature of flow sheets, showing together with the manipulative tools and materials worked upon, the various successive steps in my process for preparing a substantially hydrogen free-arc tube. -In each of the several figures of the drawings, similar numerical designation are indicative of similar elements.

Of these drawings:

FIGURE 1 is an elevational view of an arc tube cylinder having extensions disposed at either end thereof which is suitable for use according to my invention.

FIGURE 2 is an elevational view of the arc tube assembly having a purge gas line attached to the exhaust sernbly immediately prior to sealing while the glass is still hot.

FIGURE 5 illustrates the cooling of the glass after sealing but before the extension has been removed.

FIGURE 6 is an elevational view of the arc tube during heating of the other end of the arc tube in preparation for sealing. j r

FIGURE 7 is an elevational view of the sealing techniques used upon the heated quartz envelope.

' FIGURE 8 is an elevational view of cooling the arc tube after sealing. v

FIGURE 9 is a side elevational view of the high pressure electric discharge device sealed according to my invention.

Referring now to FIGURE, 1, the arc tube cylinder 1 has extensions 3 and 4 exposed at either end thereof and an appended exhaust tube 2 disposed in the middle. To fabricate the assembly, I prefer to mount an extension in the chuck of a lathe and mount the arc tube cylinder having an exhaust tube appended to the side thereof upon another chuck of the lathe in a manner so that the axis of l the arc tube cylinder coincides substantially with the the softening point, the two pieces are joined together. A similar operation is then repeated with the other ex-' tension and the other side of the arc tube. The exhaust tube is so disposed that the bore thereof if in'communh" cation with the interior of the arc tube cylinder so that flush and fill procedures may be used so that materials may be added easily to the arc tube after the ends have been sealed.

Although the preferred embodiments of our invention utilizes an extension which is neckeddown to a diameter of about three quarters to one quarter of the diameter of the arc tube cylinder, it is quite possible to use the extensions which have substantially the same diameter. However with smaller diameters, these extensions tend to interfere with any upward flow of hydrogen into the arc tube and hence are quite beneficial. I prefer to use extensions which are approximately one half the diameter of the arc tube cylinder. As to their length I have discovered that they should be greater than about one inch if entry of hydrogen is to be reduced. Longer extensions may be used and I have determined that about 2 inches is quite satisfactory from the standpoints of reduction of hydrogen inclusion and cost.

Referring now to FIGURE 2, the arc tube assembly is disposed upon a pedestal 9 and is supported by clamps (not shown) in such a manner so as to space the end of the extension 4 from the pedestal base 10. Mounted in holes drilled in the pedestal 9 is a conventional electrode assembly 5 having an electrode 6 with a molybdenum foil 7 and lead-in wire 8. Surrounding the extension 4 and hence the pedestal 9 which is inserted the-rein, is a flame proof baffle plate 11 having an aperture therein. The plate 11 is preferably made of quartz or a similar high melting material or metal so that during heating of the quartz, in which flames issue forth from heating burners, they will be baffled away from flowing into the arc tube cylinder; that is their normal downward flow path will be disrupted.

After placing the arc tube assembly upon the pedestal 9, a source of gas such as nitrogen which non-deleterious to components of the lamp, is passed into the arc tube through the exhaust tube 2 by means of hose 12. At the end of the arc tube extension 3, I place a loosely fitting stopper 12, generally a conically shaped glass member, however this is not critical, to reduce the escape of the nitrogen through the end of the arc tube which is not being sealed.

After the arc tube assembly has been completely filled with nitrogen, the next step is to heat the arc tube to softening as shown in FIGURE 3. In order to attain such heating, I prefer to dispose a pair of burners 20 and 21 about the arc tube assembly. The burner heads which I prefer to use are water cooled, as is conventional in the art, so that the heat will not cause any damage to their structure. As shown, the arc tube assembly is vertically oriented and the scaling is preferably done at the lowermost side of the arc tube cylinder 1 so as to prevent any combustion gases from rising and entering the arc tube assembly and further to prevent the arc tube extension from falling over when the glass is softened. The flames 22 from the burners 20 and 21 will issue forth around the arc tube cylinder and travel downwardly on the extension 4 where they will hit bafiie plate 11. Only a small amount of combustion gases will pass through the aperture disposed in the baflie plate 11 and hence only negligible quantities can even reach the end of the arc tube extension 4. When the glass is soft, the arc tube extension will drop down slightly so that the end will touch the pedestal base 10. The flow of the nitrogen is not inhibited by this dropbecause I provide a series of radial grooves 23 in the base thus allowing for outward gaseous diffusion.

Following the softening of the glass, burner heads are withdrawn and a pair of sealing jaws are stamped against the glass as shown in FIGURE 4. These jaws 24 and 25 will close upon the heated cylinder and the extension so as to form a conventional seal. Stopper 12 counterbalances the restriction caused by the electrode holder therefore giving uniform flow of nitrogen flush-ing gas around the electrode and hence providing a protective atmosphere. Nitrogen pressure is shut off at the instant of pressing and started again as soon as the glass solidifies to protect the electrodes from oxidation during the cooling cycle.

After the seal has been formed, the glass is cooled as shown in [FIGURE 5 by placing the seal directly ina blast of cold air. When sufficiently cool to be handled the extension is gently broken olf so as to form a conventional arc tube seal and the arc tube cylinder with one extension is then mounted in clamps (not shown) as illustrated in FIGURE 6. Sealing of the lower end of the other end of the arc tube is made in a manner similar to that described with reference to FIGURE 3. The glass is softened by burners 20 and 21 when the arc tube 1 and extension 3 is mounted upon the pedestal 9 which has conventional electrodes disposed therein. Upon softening of glass, the extension 3 sags upon the base 10 as shown in FIGURE 7. The press seal is again made in the manner as described above so as to form an arc tube envelope such as shown in FIGURE 8 wherein a blast of cold air 26 is directed to the seal so as to cool it and prepare it for easy breaking.

When cool, the ends of the arc tube are broken olf so as to form the conventional arc tube envelope such as shown in FIGURE 9 wherein a pair of electrodes 6 and 27 and starting probe 28 is sealed through opposite ends of a quartz envelope and therein the exhaust tube 2 is disposed upon the envelope wall.

It is apparent that modifications and changes may be made within the spirit and scope of the instant invention, but is my intention however to be limited only by the scope of the appended claims.

As my invention 1 claim:

1. In the process of manufacturing an iodine containing arc tube for use in a high pressure discharge device, the steps which comprise: forming an arc tube assembly of an arc tube cylinder with an extension disposed at either end thereof said are tube and extension being formed of a high silica content glass; placing an electrode supported by a lead-in wire within said are tube assembly and introducing a purge gas which is nondeleterious to the metal components of said device; heating said are tube assembly to softening with flames from a burner at a point adjacent the joint of said extension and said are tube cylinder, substantially excluding combustion gases, including any. hydrogen contained therein, by deflecting said combustion gases away from the interior of said are tube cylinder; press sealing the softened glass of said are tube about said lead-in wire.

2. The process according to claim 1 wherein the arc tube assembly is substantially vertically oriented and the heating and the sealing is performed upon the lower portion thereof.

3. The process according to claim 1 wherein at least some of the combustion gases flow downwardly along said extension and are redirected outwardly in their flow, said redirection being caused by a baflle disposed closely below the point where the burner flames contact the arc tube assembly.

4. In the process of manufacturing an iodine containing arc tube for use in a high pressure discharge device, the steps which comprise: forming an arc tube assembly of an arc tube cylinder having extensions of smaller diameter than said arc tube cylinder disposed at either end thereof and having an exhaust tube disposed on said are tube cylinder in communication with the interior thereof said are tube and extension being formed of a high silica content glass; placing an electrode supported by a lead-in wire within said are tube assembly and introducing a.

purge gas which is non-deleterious to the metal components of said device; heating said are tube assembly to softening with flames from a burner at a point adjacent the joint of the extension and the arc tube cylinder, substantially excluding combustion gases, including any hydrogen contained therein, by deflecting said combustion gases away from the interior of said are tube cylinder; press sealing the softened glass of said are tube assembly about said lead-in wire.

5. The process according to claim 4 wherein the extensions are one quarter to three quarters of the diameter of the arc tube cylinder.

6. The process according to claim 4 wherein the arc tube assembly is substantially vertically oriented and the heating and the scaling is performed upon the lower portion thereof.

7. The process accord-ing to claim 4 wherein at least some of the combustion gases flow downwardly along said extension and are redirected outwardly in their flow, said redirection being caused by a baflle disposed closely below the point where the flames contact the arc tube assembly. a

8. In the process of manufacturing an iodine-containing arc tube for use in a high pressure discharge device, the steps which comprise: forming an arc tube assembly of an arc tube cylinder having extensions of smaller diameter than said are tube cylinder disposed .at either end thereof and having an exhaust tube disposed on said are tube cylinder in communication with the interior thereof said are tube and extension being formed of a high silica content glass; vertically orienting said arc tube assembly;

' placing an electrode supported by a lead-in wire within said vertically oriented are tube assembly and introducing and maintaining a purge gas which is non-deleterious to the metal components of said device; heating the lower portion of said arc tube assembly to softening with flames from a burner at a point adjacent the joint of the extension and the arc tube cylinder substantially excluding combustion gases, including any hydrogen contained therein, by deflecting said combustion gases away from the interior of said are tube cylinder; press sealing the softened glass of said are tube assembly about said leadin wire; inverting said arc tube assembly and heating the glass to softening with flames from a burner at a point adjacent the joint of-the remaining extension and the arc tube cylinder, substantially excluding combustion gases, including any hydrogen contained therein, 'by defleeting said combustion gases away from the interior of said are tu'be cylinder sealing said softened glass about said lead-in Wire.

9. The process according to claim 8 wherein the arc tube extensions are one quarter to three quarters the diameter of said are tube cylinder.

10. The process according to claim 8 wherein at least some of the combustion gases flow downwardly along said extension and are redirected outwardly in their flow, said redirection being cause by a baffle disposed closely below the point where the flames contact the arc tube assembly.

References Cited by the Examiner UNITED STATES PATENTS 1,655,820 1/1928 Perryman 56 2,215,641 9/1940 Freeman 65-155 X 2,235,515 3/1941 Carpenter 65-56 X 2,491,237 12/ 1949 Way 6532 2,496,303 2/1950 Morse et a1. 6556 X 3,113,010 12/1963 Willis et a1. 65139 X DONALL H. SYLVESTER, Primary Examiner.

R. L. LINDSAY, Assistant Examiner. 

1. IN THE PROCESS OF MANUFACTURING AN IODINE CONTAINING ARC TUBE FOR USE IN A HIGH PRESSURE DISCHARGE DEVICE, THE STEPS WHICH COMPRISES: FORMING AN ARC TUBE ASSEMBLY OF AN ARC TUBE CYLINDER WITH AN EXTENSION DISPOSED AT EITHER END THEREOF SAID ARC TUBE AND EXTENSION BEING FORMED OF A HIGH SILICA CONTENT GLASS; PLACING AN ELECTRODE SUPPORTED BY A LEAD-IN WIRE WITHIN SAID ARC TUBE ASSEMBLY AND INTRODUCING A PURGE GAS WHICH IS NONDELETERIOUS TO THE METAL COMPONENTS OF SAID DEVICE; HEATING SAID ARC TUBE ASSEMBLY TO SOFTENING WITH FLAMES FROM A BURNER AT A POINT ADJACENT THE JOINT OF SAID EXTENSION AND SAID ARC TUBE CYLINDER, SUBSTANTIALLY EXCLUDING COMBUSTION GASES, INCLUDING ANY HYDROGEN CONTAINED THEREIN, BY DEFLECTING SAID COMBUSTION GASES AWAY FROM THE INTERIOR OF SAID ARC TUBE CYLINDER; PRESS SEALING THE SOFTENED GLASS OF SAID ARC TUBE ABOUT SAID LEAD-IN WIRE. 